This is a bug I and others have reported in 12.1.0 and 12.1.1 - custom workspace order isn't remembered and switching between workspaces, especially custom workspaces and coming from the Color workspace, cause PP to hang.
Win 10, Intel last gen 6 and 8 core, 32 and 64GB RAM, SSD OS, pagefile/Temp/ Cache and preview drives, RAID5 or 6 spinning drives, GTX 980 and 1080ti.